1. Field of the Invention
The present invention relates to a capsule type endoscope that is introduced into a subject and transmits subject internal information to an external receiving device while moving in the subject with the subject being used as a signal transmission medium.
2. Description of the Related Art
Presently, in the endoscopy field, a capsule type endoscope which is of a swallowable type is in practical use. The capsule type endoscope has an imaging function and a wireless communication function. Further, after the capsule type endoscope is introduced from a mouth of a subject for observation (inspection), it sequentially performs imaging while moving in an organ, e.g., a stomach or a small intestine in accordance with its peristaltic motion until it is naturally excreted, thereby acquiring information of the inside of the subject.
Subject internal information (image data) obtained in a body while the capsule type endoscope moves in a body cavity is sequentially transmitted to the outside based on wireless communication, and stored in an external provided memory. When the subject takes along a receiver including a wireless communication function and a memory function, he/she can freely move after swallowing the capsule type endoscope until the capsule type endoscope is excreted.
Furthermore, as one of wireless communication modes in the capsule type endoscope, a human body communication mode of utilizing a subject as a signal transmission medium to transmit image data to the outside has been proposed. For example, in JP-A 2006-513670 (KOKAI), two signal electrodes are provided on the outer peripheral surface of a capsule type endoscope, and a potential difference according to image data is produced between the two electrodes to cause a current to flow through a subject. Moreover, when the amount of current flowing between the receiving electrodes of an external receiving device arranged outside the subject is detected, the image data can be transmitted by utilizing the human body as a signal transmission medium.
Here, the capsule type endoscope disclosed in JP-A 2006-513670 has a configuration where transmitting electrodes are arranged on the outer surface, contact states of the transmitting electrodes of the capsule type endoscope put in the subject vary when moving in the subject. As a result, the impedance between the transmitting electrodes used to transmit a transmission signal of the capsule type endoscope also varies in the subject. Therefore, impedance mismatch between the transmitting electrodes and the subject occurs with respect to a change in the impedance between the electrodes, and a loss of a transmission signal power of the capsule type endoscope may possibly occur.
On the other hand, in JP-A 2006-513670 (KOKAI), a control method with respect to a change in the impedance between the transmitting electrodes is not explained in particular, and the loss of transmission signal power readily leads to a reduction in a reception signal level. Therefore, the reception signal is easily affected by noise, and stability of communication as a capsule type endoscopic system is apt to be degraded.